DC motors are well known and used in a wide variety of functions and industries. In general, such motors utilize a changing magnetic field that causes an inner shaft or rotor to rotate relative to an outer body or stator, which is usually fixed. Typically, the rotor is permanently magnetized, while a series of poles encircles the rotor, the poles wound with wire or "windings" so as to create a magnetic field when current flows in the wire. Current is supplied to the windings to create a magnetic field near the poles that attracts or repels the rotor, causing the rotor to revolve.
To better control the motion of the rotor, information regarding actual or measured parameters of the motion can be used to vary the input current in order to approach or achieve desired motion values. Such a servo control system may employ a microprocessor, power supply and amplifiers for controlling the current to the windings, position or motion detectors for determining the actual position or motion of the rotor, and wires for relaying signals between the controller, amplifiers, windings, detectors and power supply. For some applications it is desirable to have a motor in close proximity to a controller.
For example, in U.S. Pat. Nos. 5,107,387 and 5,136,452, Orton discloses a radio controlled model race car having a controller coupled to a DC motor used to drive the car, and various fuse and circuitry devices for connecting the motor and controller and for braking the motor. U.S. Pat. No. 5,237,540, to Malone teaches a brushless DC motor used for drilling having an encoder coupled to the motor for sensing a position of the motor. Similarly, U.S. Pat. No. 5,249,161 to Jones et al. dis-closes a borehole driller having means for determining whether an encoder and position sensor attached to the motor is jammed. In U.S. Pat. No. 5,159,218, Murry et al. teach a solid state controller mounted directly to a brushless DC motor for pumping fluids in environments which may be encountered during space missions.
Having a controller close to a motor may still require extensive interwiring. As shown in FIG. 7, a typical servo motor control system has a motor 20 with an encoder 22 attached to the motor for determining the position of the motor 20. A servo controller 25 and an amplifier 27 are separated from the motor 20 and encoder 22, but connected by a multiplicity of wires. The servo controller 25 is supplied with power and ground wires 30, and the servo controller 25 is wired to a host via separate transmit and receive wires as well as a ground 32. The amplifier 27 is separately supplied with power and ground wires 33, and has a number of potentiometers 28 for adjusting the amplifier 27. The servo control 25 and the amplifier 27 are connected with a set of wires 35 including those for a command signal, a shutdown signal, an error signal and ground. Wire connections 37 between the encoder 22 and the servo controller 25 include power and ground and six signal wires. Wires 39 connecting between the motor 20 and the amplifier 27 include a power and a ground wire for a Hall sensor in the motor 20, a pair of Hall sensor signal wires, and individual wires for three motor phases. The web or harness of wiring shown in this figure may be difficult to correctly connect and noise from high current wires powering the motor may disrupt sensitive signals in nearby wires used for servo control.
It is an object of the present invention to provide a simple and reliable servo motor having improved precision of motion due to improved mechanical and electrical connection between the motor and controller.